A light-emitting element (also referred to as an organic EL element) using organic EL has been actively researched and developed. In the fundamental structure of an organic EL element, a layer containing a light-emitting organic compound is provided between a pair of electrodes. By voltage application to this element, light emission from the light-emitting organic compound can be obtained.
An organic EL element, which has characteristics such as feasibility of being thinner and lighter, high speed response to input signals, and capability of direct current low voltage driving, has been expected to be applied to next-generation flat panel displays or lighting devices. In particular, a display device in which organic EL elements are arranged in matrix is considered to have advantages of a wide viewing angle and excellent visibility over a conventional liquid crystal display device.
However, an organic EL element has a problem in that entry of impurities such as moisture or oxygen from the outside erodes the reliability.
When impurities such as moisture or oxygen enter an organic compound or a metal material contained in an organic EL element from the outside of the organic EL element, the lifetime of the organic EL element is significantly shortened in some cases. This is because an organic compound or a metal material contained in the organic EL element reacts with the impurities such as moisture or oxygen and thus deteriorates.
Thus, a technique to seal an organic EL element for preventing entry of impurities has been researched and developed.
An organic EL element can be sealed with a thin film, glass using glass frit or the like, or a resin, for example. The technique to seal an organic EL element with a thin film has problems such as high cost and low productivity. The sealing property of a resin is lower than that of glass and it is difficult to completely block impurities such as moisture or oxygen. In contrast, it is considered that a technique to seal an organic EL element with a pair of substrates and glass using glass frit or the like is a preferable sealing method because of its low cost and high productivity.
For example, a glass package sealed by attaching a first glass plate to a second glass plate with frit, which can be applied to seal an organic EL element, is disclosed in Patent Document 1.